Overview of Australia’s marine environment
The diversity of three oceans, five climate zones, varied underwater seascapes and mighty currents bring together a trove of ocean treasures.
With a coastline stretching 70,000 kilometres, Australia has an incredibly diverse marine environment that rivals that of any other nation.
The Global Census of Marine Life ranks Australia number one for marine biodiversity, with more species recorded than any other country. Thirty-three thousand marine species are known to occur in Australian waters, including 8525 molluscs, 6365 crustaceans and 5184 fishes (20 per cent of the total global number of fish species).
Importantly, many of these species are found only in Australia; for instance, up to 80 per cent of the fish on our temperate coasts are unique to our nation. The seabed with its shallow waters, continental shelves, slopes, plateaus and abyssal plains provides a wide range of habitats for plants and animals. These seabed habitats are also important in supporting ocean productivity. For instance, upwellings of nutrient-rich waters around undersea canyons support biodiversity hotspots where high numbers of feeding seabirds, whales and dolpins are present.
One of Australia’s most remarkable natural gifts, the Great Barrier Reef is the world’s largest coral reef. It has an abundance of marine life and comprises over 3000 individual reef systems and coral cays and hundreds of picturesque tropical islands.
Australia’s east and west coasts are migration routes for a range of threatened species. For example, the line of shelf-canyons on the west coast of Australia is a “whale highway”, where thousands of humpback whales travel annually on their migration from their Antarctic feeding grounds to their breeding grounds in northern Australia and back again.
Marine parks are the backbone of biodiversity protection. However, less than five per cent of the Australian marine environment is in fully protected marine sanctuaries (where mining and fishing are prohibited), compared with more than 10 per cent of our land area. This falls well short of the 20 to 50 per cent recommended internationally for long-term ocean health. Marine-based industry contributes about four per cent of Australia’s GDP and is increasing rapidly. Industries include:
- energy production (oil and gas extraction)
- fishing and aquaculture
- recreation and tourism
- emerging industries such as seabed mining, carbon capture, desalination, tidal and wave power, and the use of marine organisms for new materials or pharmaceuticals.
Our marine economy supports thousands of jobs, but the oceans also provide $25 billion every year in services including:
- carbon storage at about $15.8 billion a year. Seagrasses store 10 to 40 times as much carbon per hectare as forests. Australia’s seagrass meadows are the largest in the world.
- fish nursery services, pest and disease control — $6.2 billion. These are crucial for our commercial fishing industry.
And finally, healthy oceans are essential to life on our planet. According to some estimates, green algae and cyanobacteria provide 20 per cent of the oxygen produced on Earth.
The state of our marine environment
The overall health of our marine environment is good, but this largely reflects the condition of offshore waters and remote coastlines. Along our developed coasts, particularly in the southeast, ecosystems are in poor health due to:
- commercial and recreational fishing
- coastal, urban, industry and port development, including the expansion of oil and gas
- invasive pests and diseases
- algal blooms
- sediment and nutrient loads to coastal waters are excessive
- worrying levels of pesticide in water near intensive agriculture
- the legacy of poor management.
Pressures are region-specific. Largely undisturbed habitats in the northwest are affected by oil and gas industry expansion, whereas development and fishing are the main threats on the populated sections of the eastern and western coastlines.
Our coastal and marine environments are used by everyone, but their management is poorly coordinated and they are consequently suffering from ‘death by a thousand cuts’. As climate change intensifies, it is even more urgent that we develop a nationally coordinated approach to our marine environment and avoid the management failures of the past.
Some Australian marine habitats are dead as a result of heavy pollution. These include mining waste-damaged Darwin Harbour and Melville Bay in the Northern Territory.
The loss of about 30 per cent of our seagrass areas and the degradation and loss of mangroves is also concerning. Seagrass beds occur in many coastal waters and estuaries, and offshore down to 50 metres depth. They act as nurseries for the young of some crustacean and fish species including yellowfin, bream, luderick and leatherjacket.
About two-thirds of eastern Australia’s commercially caught fish and prawns depend on mangroves, but these habitas are under threat from development. Mangroves also protect shorelines from damaging storms, waves and floods. Their dense, tangled root systems help maintain water quality, filtering pollutants and trapping and stabilising sediments.
Destructive fishing techniques such as trawl fishing continue damaging key fish habitats as well as being destructive to non-target species caught as “by-catch”.
The southeast is the only region where an entire habitat type has been made extinct: the oyster reef beds that used to dominate some estuaries and small bays. This loss has affected other species and probably reduced water filtration and removal of pollutants.
In the southeast, sediment, nutrients and toxics inputs have significantly degraded ecosystem functions in the Coorong, the Derwent River and estuary and the Gippsland Lakes.
Biodiversity loss in the marine environment
The sea floor is the largest but least-known ecosystem on Earth. Much of our knowledge of marine biodiversity is centred on fished species where records have been kept over long periods of time.
In comparison, we have limited understanding of non-fished species and their roles in maintaining healthy and resilient oceans and as such the status of our fished species is a surrogate for the status of our biodiversity.
Worryingly, many Australian fisheries are far from sustainable, despite improvements in the past three decades. Intense fishing in the past and current fishing practices mean most sought-after species are at low numbers and either not recovering or recovering very slowly. These include orange roughy, southern bluefin tuna, toothed whales, whale sharks and great white sharks.
Marine reserves help protect fish and allow their numbers to recover. More than 30 per cent of the Great Barrier Reef Marine Park is now a no-take marine reserve. Coral trout on reefs closed to fishing have recovered very quickly from earlier intensive fishing.
Threats and pressures facing Australia’s marine environment
Climate change is the major threat looming over our oceans and coastal waters. Its key impacts come from:
- increased ocean temperatures
- ocean acidification
- increased incidence of extreme weather and sea level rises.
Australian ocean temperatures have warmed since the early 20th century by 0.7˚C. Six of the ten warmest surface temperatures on record have occurred in the past ten years. By the 2030s, water surface temperatures are predicted to be around 1˚C higher (relative to 1980-99).
Rising ocean temperatures in Australia force species southward. This will eventually mean major decline for southern coastal species that require shallow, cool water. Further loss of seagrass meadows and algal beds are expected due to warmer water, storms and turbidity.
Higher temperatures cause coral bleaching and disease outbreaks. Coral bleaching happens when a coral expels its zooxanthellae, the marine algae that live in symbiosis with corals. This results in the death of the coral.
Coral is the base habitat for much of the marine biodiversity of a reef. Many other organisms are badly affected by coral bleaching. Butterfly fish appear to survive for no more than five years after severe coral bleaching.
Increased carbon dioxide in the atmosphere forms a weak acid in water. Some organisms such as corals, sea-shells, crustaceans and sea urchins are vulnerable to acidification because it reduces their ability to make shells.
Ocean acidification also poses a risk to marine food chains. There have already been changes detected in calcification not only of Great Barrier Reef coral, but also Southern Ocean zooplankton, which are a key link in the marine food chain that goes all the way up to some of our most highly valued fish species.
Around half the oxygen in the atmosphere is produced by oceans. Acidification is likely to affect microscopic organisms such as “coccolithophores” that help make oxygen. This may well have a critical impact on the mix of carbon and oxygen in the atmosphere.
Extreme weather and sea level rises
With climate change comes increased frequency of natural disasters. Queensland’s 2011 floods destroyed three of the four major seagrass feeding grounds of the vulnerable dugong. The dugong death toll in 2011 was 1048, compared to 555 in 2010, with most deaths attributed to starvation.
There has been substantial loss of coastal land due to sea level rises. Intrusion of salty water into coastal waterways and wetlands also threatens habitats and ecosystems.
Fishing and aquaculture
Some of the largest commercial fishing operations in tropical marine waters are those targeting prawns, scallops and slipper lobsters. Trawl fishing involves dragging a net across the seabed, creating a cloud of muddy water and “clear-felling” the sea floor of animals and plants. For every kilogram of fish, up to five kilograms of other marine life including sponges, shells, crustaceans and molluscs are inadvertently caught by some trawlers.
Other destructive fishing practices such as longline fishing for tuna and gill netting for sharks are also widespread in Australia’s waters. They take a heavy toll on some of our most threatened marine species.
In 2009, 12 per cent of the species managed by the Australian Fisheries Management Authority were assessed as overfished and 10 per cent as suffering from ongoing overfishing. In addition, not enough was known about the numbers of about a third of the species being fished.
Intense fishing of a species has cascading effects. Persistent low populations:
- make the species vulnerable to other pressures such as climate change (for example by reducing the breeding stock) and habitat loss
- have flow-on effects for the resilience and persistence of marine biodiversity (for example by taking top-level predators out of the food chain).
Despite this, there is no nationally integrated analysis of the cumulative impacts of fishing on ecosystems. And there are no national assessments of the ecological sustainability of commercial or recreational fishing.
Coastal development and new fishing technology (such as greater access to bigger recreational fishing boats, and fish-finding sonar systems) have removed refuges that once existed in remote places or where the seabed was formerly too rugged to be fished.
The accidental capture and drowning of sea lions and dolphins is also a significant problem in net fisheries off Australia’s south coast.
Recreational fishing also places pressure on the marine environment. Recreational catches can be larger than commercial catches for many sought-after species.
Australia has a small but growing aquaculture industry, which includes Atlantic salmon farmed in cages off the Tasmanian coastline, and the fattening of young wild-caught southern bluefin tuna (known as “tuna ranching”) in the Spencer Gulf off the South Australian coast. Farmed fish such as salmon and tuna have high protein needs which are mostly met by feeding them wild-caught fish, depleting the stocks of these “forage” species.
The main areas of concern with respect to aquaculture are the:
- potential for spread of diseases and parasites such as sealice from caged salmon to wild fish
- waste, including nutrient enrichment of the seabed around cages from excess feed
- escape of farmed fish and shellfish into the natural environment
- source and sustainability of wild-caught fish to stock farms and for use as feed
- use of chemicals, antibiotics and antifoulant paints.
Aquaculture in Australia has caused major outbreaks of disease in wild fish. These have left lasting imprints on some ecosystems.
Pests, algal blooms and diseases
Introduced marine plants and animals arrive into Australian waters on all types of ships, carried on hulls and in ballast waters and inside internal seawater pipes. They are also introduced via aquaculture, aquarium imports, marine debris and ocean currents. Once marine pests are established, eliminating them is virtually impossible. They can multiply quickly and force out native species. Some, such as toxic algae, can pose a threat to human health.
Pests in southeastern Australian waters include some species of starfish, sea urchins, plankton, algae, molluscs, crustaceans and worms. Port Phillip Bay has been described as one of the most invaded marine ecosystems in the southern hemisphere, but there are others of equal note, including the Derwent estuary. Periodic outbreaks of harmful native species also occur elsewhere around Australia, such as crown-of-thorns starfish and algal blooms in Moreton Bay near Brisbane.
Oil, gas and shipping
In Australia, oil and gas industries are concentrated in Bass Strait and northwestern Australia, with developments expanding into other regions.
The marine environment is disturbed by:
- seabed structures such as wellheads, anchors and pipelines
- shipping traffic
- accidents and spills
- ocean noise pollution from underwater seismic exploration
- industrial sites, ports and processing and maintenance facilities.
Dredging of the sea floor near the shoreline has serious impact. In Western Australia alone, more than 200 million cubic metres (the equivalent of nearly half the water in Sydney Harbour) of dredge spoil has recently been approved for disposal in the deeper ocean and along the coast.
The Montara spill in August 2009 was Australia’s worst offshore exploration oil accident. For 74 days, oil and gas flowed into the Timor Sea at a rate of at least 64 tonnes a day. The accident exposed inadequacies in governance, science and logistics.
The management of oil and gas expansion is poorly coordinated. Each development is considered on its own merits with little thought for cumulative impacts across a region.
The shipping industry is expanding with many new ports being built and existing ports being expanded. Much of this is supporting mining growth in Queensland, the Northern Territory and Western Australia.
Expanding ports can require dredging and major development in sensitive areas and can lead to habitat destruction, death or injury to marine species, the spread of toxins and noise pollution.
Shipping lanes traverse some of the most ecologically sensitive marine areas, and there are regular grounding and other accidents at sea that harm the marine environment. Ships frequently hit marine mammals in open waters.
As oil-industry shipping intensifies in the northwest, the “whale highway” migration route of humpback whales is likely to be affected. Despite this, there are still no upper limits on the size of ships, shipping lane use, frequency of transit or seasonal constraints.
Noise from shipping and sonar used in defence exercises may also harm whales and dolphins.
Runoff and land-based pollution
Nutrients and sediment from human activity can lead to the decline of coastal water quality. Water quality is poor in a high proportion of New South Wales estuaries. This is directly linked to the fact that more than half the estuaries in New South Wales are subject to double the natural sediment and nutrient inputs and around one-third of all the catchments in the state have been cleared of more than 50 per cent of their natural vegetation.
On the Great Barrier Reef, the quality of water entering the reef continues to drop. The 38 river catchments emptying into Great Barrier Reef waters deliver:
- two to ten times more nutrients and sediment than before European settlement
- agricultural chemicals, including fertilisers, pesticides and herbicides.
This excess can cause algal blooms and the suffocation of reefs. It also increases the susceptibility of reefs to outbreaks of coral-eating crown-of-thorns starfish. These impacts are then potentially passed on further up the food chain to turtles, dugongs and predatory fish.
In 2010 Achim Steiner, the executive director of the United Nations Environment Programme (UNEP) said:
If collectively we carry on using the seas and oceans as a dustbin, human beings will soon have turned the once beautiful and bountiful marine environment from a crucial life-support system into a lifeless one.
According to the UNEP, 8 million items of litter enter the oceans and seas every day, about five million (63 per cent) of which are solid waste thrown overboard or lost from ships. More than 13,000 pieces of plastic float on every square kilometre of the world’s oceans.
The UNEP estimates that every year 100,000 turtles and marine mammals such as dolphins, whales and seals are killed by swallowing or becoming entangled in plastic.
Marine debris has a significantimpact on Australian vertebrate marine lifeand the Federal Government has developed a Threat Abatement Plan for it.
High concentrations accumulate on coasts close to cities and have also been reported at some remote areas including Cape York, Groote Eylandt, northeast Arnhem Land and the far north Great Barrier Reef.
Plastic bands or net fragments entangled around the necks of young animals restrict their ability to feed properly and, as the animal grows, strangle and kill them. Abandoned fishing gear, ropes and other debris tangled around animals can lead to infections, restricted mobility, slow amputation of limbs and death through drowning, starvation or smothering.
Swallowed litter can starve animals by making it hard to digest food, causing internal wounds and ulceration or making them more buoyant and inhibiting diving.
Marine wildlife absorb toxins by swallowing “microplastics”. Microplastics are small particles that come from the weathering of larger plastic items and from the use of plastics in other processes, such as the plastic “sand” used to remove paint from ship hulls. Plastics are a particular threat because they are slow to break down, even more so in the ocean than on land.
Plastic debris spread toxic chemicals such as polychlorinated biphenyls (PCBs) into marine food webs. These chemicals are known to compromise immunity and cause infertility in animals even at very low levels.
In Australia, 77 species are known to be affected by marine litter. These include whales, sharks, sea birds and turtles. Because turtles have spines that face downwards in their throat, they cannot cough up swallowed litter.
What philanthropy can do
Solutions to the challenges are diverse. The following is a sample of the more important responses.
We can protect the marine environment by
- creating a system of marine national parks or sanctuaries free of extractive uses – just like national parks on land, this system should include each type of habitat and protect critical breeding, feeding and resting areas of our ocean life
- ensuring our oceans are better planned and managed and ecologically sustainable
- raising awareness about the state of our marine environment
- supporting pilot projects that demonstrate regional solutions.
Reduce and manage impacts on the marine environment by
- strengthening enforcement of laws and regulations (e.g. policing of illegal fishing)
- reducing land-based sources of ocean pollution, including agricultural chemicals and debris
- stopping water quality decline on the Great Barrier Reef by repairing land along nearby riverbanks
- maintaining ground cover in river catchments and minimising agricultural runoff
- tightening controls on shipping in particularly sensitive areas such as the Great Barrier Reef and identifying solutions to other shipping issues such as ocean noise, increased turbidity and invasive species
- limiting coastal development, including new port facilities, in particularly sensitive areas
- reducing carbon emissions
- minimising the threats posed by invasive species.
Manage the impacts of oil, gas and mining by
- improving the way we manage accident risk including establishment of baselines, spill monitoring, modelling, forecasting, emergency response and environmental risk assessment
- connecting oil and gas industry planning and regional environmental management
- assessing and potentially stopping risks such as seabed mining for ores and heavy metals
- assessing and managing risks associated with the expansion of shipping.
Manage the impacts of fishing and aquaculture by
- changing Australian fisheries so there are fewer boats but improved sustainability and profitability
- banning destructive fishing techniques such as trawling
- limiting destructive fishing by buying fishing licences
- ending targeted shark fishing
- addressing the impacts of recreational fishing as part of the overall management of Australian fisheries
- creating a movement for sustainable fishing with information and tools for consumers and seafood suppliers
- supporting the establishment of sustainable aquaculture focused on species that can be produced through lower impact systems and provide consumer advice on this.
Further the knowledge base on the marine environment by
- investing in marine sciences and research that improves management and builds our understanding of temperate and tropical marine systems
- supporting research that demonstrates the benefits of marine conservation.